Bone marrow examination

Bone marrow examination

Bone marrow examination is useful in the assessment of composition, cellularity and maturation of haemopoietic cells. It is necessary when peripheral blood examination fails to provide a clue for the diagnosis of a haematological disorder, or when further information is needed on a diagnosis reached by peripheral blood smear examination. Bone marrow examination is a must when there is an unexplained pancytopenia or cytopenia of a blood cell series. It is useful in the follow up of patients undergoing therapy for malignancies.

Site of Aspiration

The bone marrow is aspirated from the medullary cavity by penetrating the cortical bone. The sternum and the iliac crest are the most common sites. Spinuous processes of vertebrae may be used. In infants and young children the medial aspect of the upper end of the tibia may be used.

Materials

2% lignocaine without adrenaline (2-5 ml)

Syringes 2 ml and 5 ml.

 Needles 21, 22 and 25 gauge.

Marrow aspiration needle with a sliding or screw guard

10-12 clean microscope slides. EDTA bottle.

Technique

1. Select a site and position the patient appropriately.

2. Cleanse the skin with 70 % ethanol or 0.5% chlorhexidine.

3. Infiltrate the skin with 2 % lignocaine with the syringe at a right angle to the skin surface. Continue to inject the local anaesthetic till the needle touches the bone. Inject in all directions to cover about 1 cm area. Withdraw the syringe and needle and cover with a gauze swab.

4. Wait for about one minute to allow the anaesthetic to act. Check that the aspiration equipment is functioning properly.

5. With the bevel uppermost, and stylet in, insert the marrow needle at right angle to the bone surface, and advance till the bone is touched. Lower the guard to l cm above the skin surface. With a firm pressure, push and rotate the needle through the cortex. The resistance suddenly ends when the needle reaches the medullary cavity. Continue advancing until the guard touches the skin.

6. Withdraw stylet and attach a 20 ml syringe. Aspirate the marrow quickly applying continuous suction. Remove the syringe and the needle, keep the area of aspiration under pressure with a gauze swab and apply an adhesive dressing.

7. After disconnecting the needle from the syringe, quickly prepare 10-12 smears of the aspirated bone marrow. The contents of the syringe are emptied into a glass petri dish. With a glass spreader pick up the yellowish particles of marrow and spread them on clean glass slides. Work quickly to avoid marrow clotting. The preparation should not be diluted with sinusoidal blood A good bone marrow smear should contain marrow particles, leaving their trails behind while spreading the film.

8. Transfer the left over marrow to the EDTA tube and mix.Staining Stain two bone marrow films using any one of Romanowsky group of stains.Preserve the other slides for special staining procedures if necessary.

Differential Cell Count on Bone Marrow (Myelogram)

Many workers perform counts on marrow films by presenting the data in the form of a myelogram, and expressing the various cell types as a percentage. Because of the naturally renegated pattern of the bone marrow and the irregular distribution of the marrow cells, differential cell counts on marrow aspirated from normal subjects show a very wide range of normality. It is necessary to choose a proper area for differential count. The cellular trails of the fragments are considered to be idealsites.

 The examination should commence from the marrow fragments working back towards the head of the films. The particles should be examined with a low power objective with particular reference to their cellularity. Estimate whether the marrow is hypocellular, normocellular or hyperplastic.

Select a highly cellular area of the film where the nucleated cells are well stained and well spread. The cells in the cellular areas should be examined with the oil-immersion objective. Observe the stages of maturation of myeloid and erythroid components.

 Count a total number of 500 cells and record each cell type as a percentage. The normal ratio of myeloid/erythroid cells ranges from 2.5:1 to 5:1. Any abnormality in maturation, e.g. megaloblastosis, should be recorded.

In adults, about 10 % of nucleated cells are lymphocytes. Their number may be higher in children. Megakaryocytes, monocytes and plasma cells should be examined for both their number and morphology, and any abnormality should be noted.